I'm confused because I just decided to order one since they offered free overnight shipping and there was no mention of any restrictions. Are you saying that cars with a custom tune wouldn't pass smog in California? Wouldn't you just revert to the factory tune when you take it to get smog checked or seen by the dealer for warranty repairs etc?
California has extremely restrictive anti pollution regulations and does not permit any devices that will alter emission controls to be shipped there. The only possible exceptions might be restored older pre-emission controlled vehices.